test(ext/setup): cover SetupStep registry shape + clearWizardState (Plan C Phase 3)

Asserts STEPS has the six steps in canonical order, each renders non-empty
HTML and returns a teardown from attach, and clearWizardState zero-fills the
reachable Uint8Array fields before resetting state. Keeps the existing
finishSetup tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

extension/src/setup/__tests__/setup.test.ts

@@ -1,5 +1,6 @@
-import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
-import { finishSetup } from '../setup';
+import { finishSetup, STEPS } from '../setup';
+import { state, clearWizardState } from '../setup-steps';
 
 describe('finishSetup', () => {
   beforeEach(() => {
@@ -35,3 +36,47 @@ describe('finishSetup', () => {
     expect(chrome.tabs.create).toHaveBeenCalled();
   });
 });
+
+describe('setup step registry', () => {
+  it('has the six steps in canonical order', () => {
+    expect(STEPS.map((s) => s.id)).toEqual(['mode', 'host', 'connection', 'vault', 'device', 'done']);
+  });
+
+  it('each step renders non-empty HTML and attach returns a teardown', () => {
+    const ctx = { state: {} as never, rerender: vi.fn(), goto: vi.fn() };
+    for (const step of STEPS) {
+      const html = step.render(ctx as never);
+      expect(typeof html).toBe('string');
+      expect(html.length).toBeGreaterThan(0);
+      // render output must be in the DOM before attach (attach wires getElementById listeners)
+      document.body.innerHTML = `<div id="app">${html}</div>`;
+      const teardown = step.attach(document.body, ctx as never);
+      expect(typeof teardown).toBe('function');
+      teardown(); // must not throw
+    }
+  });
+});
+
+describe('clearWizardState', () => {
+  afterEach(() => {
+    clearWizardState();
+  });
+
+  it('zero-fills the reachable Uint8Array fields and resets state', () => {
+    const carrier = new Uint8Array([1, 2, 3, 4]);
+    const ref = new Uint8Array([5, 6, 7, 8]);
+    state.carrierImageBytes = carrier;
+    state.referenceImageBytes = ref;
+    state.passphrase = 'secret';
+    state.mode = 'new';
+
+    clearWizardState();
+
+    expect(Array.from(carrier)).toEqual([0, 0, 0, 0]);   // fill(0) ran on the captured ref
+    expect(Array.from(ref)).toEqual([0, 0, 0, 0]);
+    expect(state.carrierImageBytes).toBeNull();           // field reset
+    expect(state.referenceImageBytes).toBeNull();
+    expect(state.passphrase).toBe('');
+    expect(state.mode).toBeNull();
+  });
+});